The primary objective of this project is the characterization of the membrane currents that control and regulate secretion of prolactin from the lactotroph of the anterior pituitary. In particular, the relative contribution of extracellular calcium and intracellular calcium to the secretion process will be assessed. In contrast to the use of clonal lines of cells as models of lactotroph function, an immunological technique for unambiguous identification of specific subtypes of cells within dispersed heterogeneous cultures will be combined with patch-clamp electrophysiological methods in order to characterize the normal lactotroph. Since the lactotroph is subject to regulation by the cyclic physiological state of the animal, a baseline of lactotroph function will be obtained using cells from long-term ovariectomized rats. Following characterization of the baseline membrane permability properties of normal lactotrophs, the effects of activators of secretion, such as thyrotropin-releasing hormone (TRH) and vasoactive intestinal polypeptide, and inhibitors of secretion, such as dopamine, will be examined. Additionally, the ability of estradiol, a potent enhancer of basal and TRH-induced prolactin secretion, to produce long-term regulation of membrane properties will be examined. These effects will also be correlated with different physiological states of the animal. The characterization of membrane currents of normal lactotrophs and the mechanisms by which they are physiologically regulated will provide fundamental information concerning the mechanisms by which intracellular calcium concentrations and cell secretion is controlled. Such information may be of critical importance in any metabolic disorder that involves an alteration in normal cell secretory capacity such as cystic fibrosis or prolactinemia.